(This is all Frogg's stuff. I take no credit.)
GUARDIAN FORCE SYSTEM
We all remember FFVIII. The Gunblades, SEeD, That hot chick Rinoa, and if you fought it, OMEGA WEAPON! But one of the most memoriable features was its Guardian Force System. You equipped the GF and you get to summon it. They could get hurt like the party, too. They sorta recreated this with FFX, the Aeon System.
I have created the system for it that is the best of both worlds!
First off, The Guardian Force, or Esper and whatnot, is considered a Medium powered tech. A Gaurdian Force's Mp Cost is equal to it's level +2. A first Level GF has a Mp Cost of 12 (Level 3 Medium). The cost is to summon the spirit itself, rather than using it.
Once summoned, You can control the spirit and order it to use almost any action. You can have it attack, defend, or use one of its Techs. There's a cost to this. The first turn after it is summoned cost nothing, but every following turn you lose Mp equal to 25% of the initial summon cost. Level 1 GF would cause it's summoner to lose 3 Mp per turn after the first. Once you have an improper amount of Mp, the GF returns back from where it came from.
The GF grows with its summoner. Yes, that means it has stats. The Base Stats are equal to the summoner's multiplied by 3. To prevent an overpowering Level 1 Tech and such, there are placed restrictions on the max amount of points a stat can have. A GF can have a maximum of 300 points per stat, for purposes of 'deity essence'.
Lvl 1 GF = Max of 40
Lvl 2 GF = Max of 70
Lvl 3 GF = Max of 120
Lvl 4 GF = Max of 190
Lvl 5 GF = Max of 250
Lvl 6 GF = Max of 300
The GF also has formulas for its Derived Stats.
Hp = 100 + 5/ Vit (no armor bonus) + 24/ Tech Lvl
Mp = 10 + Spr (no armor bonus) + 9/ 2 Tech Lvl
Ap = Str (no weapon bonus)
Map = Mag (no weapon bonus)
Spd = 10 + 1/15 Agi
Str Dice = 1 + 1/100 Str
Mag Dice = 1 + 1/100 Mag
Accuracy = 10 + 1/5 Agi
Mag. Accuracy = 10 + 1/5 Mag
Evade = 30 + 1/5 Agi (no guard bonus)
Resist = 30 + (1/10 Vit) + (1/10 Spr)
Critical = 95 - 1/15 Agi
Max Tech Level = Mag/5
Effective immediately after the GF is summoned, the summoner becomes a background figure, and doesn't take damage. The GF takes all damage that would be directed at its summoner. Once the Mp cost of the summoner runs too low, or the GF's Hp reaches 0, the Guardian Force disappears. If it becomes unconscious (Hp is 0) it cannot be summoned back until the next day or until the summoner has a good night's rest (whichever the GM chooses). Restoration and status potions/ Techs can be used on GFs, but revival items and techs cannot.
As for the Guardian Force's Techs, they cannot learn a tech more powerful then their level plus 2. The damage they do is also based around a d10. Let me give you an example: They also have a number of Tech points to learn techs, too. They have 60 TP at first level, 100 at second, 200 at third, 450 at fourth, 700 at fifth and 1000 at sixth. If you upgrade a GF, just add the differance between the level the GF is at, and the level the GF is to achieve.
Shiva is a level 1 GF Tech. Her summoner has Str 6, Mag 13, Vit 8, Spr 10, and Agi 6 and a support skill of Magic Up. So Shiva would have Str 18, Mag 39, Vit 24, Spr 30, and Agi 18. This means Shiva would also have 220 Hp, 40 Mp, 18 Ap, 51 Map (39 + 5 + 7), 11 Spd, 13 Accuracy, 17 Mag Accuracy, 33 Evade, 35 Resist, a Critical score of 94, and a Max Tech Level of 7. Shiva would have the following Techs (as created by her summoner):
Ice (Lvl 1 Weak Attack Magic; Ice) Mp 2 Damage 2d8 + 51
Ice 2 (Lvl 2 Medium Attack Magic; Ice) Mp 6 Damage 2d10 + 77
Diamond Dust (Lvl 3 Strong Attack Magic; Area Effect, Ice) Mp 21 Damage 3d12 + 77
That is basicly how a Guardian Force would be set up. Once a summoner has reached all stats at 100, the GF, if at level 6, stops growing, because it has reached it's maximum of 300.
Hope you all use this system sometime. I haven't played it out, so if you have found a problem with the system, or have any suggestions, feel free to post, and we'll see if we can make it better.